Non-rotating linear reciprocating members for thermal regenerative machines, particularly for ones being used with Stirling Cycle machines, are subjected in use to extended periods of cyclical operation. One or more reciprocating members are typically formed in a Stirling Cycle Machine. Sliding seals and gas springs have been incorporated into such machines in order to form suitable reciprocating members. For example, Stirling cycle machines incorporate reciprocating elements with associated internal and/or external seals.
A typical application for internally mounted flexural bearing assemblies in power conversion machinery is found on a Stirling cycle electric power generator. One typical configuration of this generator has a movable displacer contained within an enclosed working chamber. The displacer forms a movable piston within the generator housing, transferring working fluid back and forth between a compression space (a low temperature space) and an expansion space (a high temperature space). A power extraction piston is provided in fluid communication with the compression space. Additionally, a fluid flow path transfers working fluid from the expansion space to the compression space through a gas heater, a regenerator, and a gas cooler, respectively.
Heat is applied to the heater head, causing the displacer to reciprocate within a cylinder between the compression and expansion spaces. As a result, working fluid is transferred cyclically back and forth through the internal heat exchangers. The working gas is cooled as it flows through the gas cooler, adjacent to the compression space, and heated as it flows through the gas heater, adjacent to the expansion space. Depending on the direction of fluid flow, the regenerator acts as an energy storage device that extracts heat from the gas passing from the gas heater to the gas cooler, and stores it for about one-half of an engine cycle. The stored heat is returned to the gas one-half cycle later as the gas flows from the gas cooler to the gas heater. External heat is supplied to the gas heater at the hot end where heat is applied by a source to the exterior of the heater head. Pressure oscillations in the compression chamber (low temperature space) cause the working piston of the linear alternator to reciprocate, creating a source of electrical power therefrom.
However, presently available construction techniques have proven costly, often requiring large amounts of machining to produce assembled components that realize desired alignment of parts upon assembly. Furthermore, present techniques often result in part assemblies that produce stack up of errors in toleranced dimensions. Also, such techniques prove difficult to manufacture and assemble. Additionally, many thermal regenerative machines have at least two independent free piston reciprocating members that cooperate, in operation, to transfer energy between an electric and a thermal state. Therefore, improvements in flexure bearing assemblies are needed.
Improvements have been made to more effectively use the Stirling cycle working space in the compression space of Stirling cycle engines and coolers. Instead of forming the displacer directly from the linear reciprocating member within such a Stirling device, attempts have been made to spring the displacer onto the working piston of the linear alternator, or alternatively, a linear drive motor. Such techniques have involved mounting the displacer via a gas spring onto the piston of the associated power generator or electric motor. Therefore, the more-traditional construction of a pair of free-pistons that communicate solely through the mutual fluid communication of a working gas is further modified to provide communication through a more self-contained arrangement of gas springs. Such construction provides a more effective use of the Stirling cycle working space in the compression space of a Stirling cycle device. Hence, reduced dead volume is provided within the device. Additionally, the manufacture of the cylinders and seals is somewhat simplified due to a reduction in required machining tolerances and/or in the number of concentric parts needed to be configured in an assembly. However, such a gas-spring arrangement of dual pistons results in a mechanical configuration that has a complex system dynamics. Furthermore, it proves difficult to properly size the displacer relative to the gas spring.
The present invention arose from an effort to simplify the manufacture of Stirling cycle machines and to improve the implementation of flexural bearings and clearance seals in such devices. More particularly, low cost assembly techniques for free piston Stirling cycle devices are desirable to provide a Stirling cycle device which can be manufactured at a lower cost, which is more readily and easily assembled, significantly reduces the machining of components, enables the use of reduced weight assemblies while still providing for utilization of flexural bearing assemblies, provides for the springing of displacers to pistons while reducing the complexity of the system dynamics produced by springing the displacer to the piston of a Stirling cycle device, has a long service life and is rugged, durable, reliable, of simplified design and of relatively economical manufacture and assembly.